RUNNING ON EMPTY:

Such fundraising pitches aren't unusual, since candidates seek to keep donors from feeling complacent, and Obama campaign spokesman Ben LaBolt characterized the conference call as "routine." But it echoes the urgent tone the Obama campaign has struck in recent appeals, which have raised the specter of Romney holding a significant cash advantage over Obama. "I will be outspent," read the subject line of a Tuesday e-mail Obama sent his supporters.

The call from Air Force One, which apparently ran afoul of no laws governing the separation of official and campaign business, came just hours before the Saturday deadline for reporting June donations.

And it was on the heels of what turned out to be a fundraising boon for Romney: the former Massachusetts governor's campaign claims to have taken in $4.6 million during the 24 hours after the Supreme Court's decision on Thursday to uphold the Affordable Care Act. The Obama campaign claims that it, too, raked in money after the decision, though the campaignhas not revealed how much.

Obama has benefited from Democratic super PACs, but they have trailed their GOP counterparts in amassing funds.

The Romney campaign raised more than Obama in May and a senior Obama official predicted to reporters two weeks ago that Romney could raise $100 million in June.

For a campaign that had the luxury of vastly outspending Sen. John McCain (R-Ariz.) four years ago, the prospect of being on the other side of a torrent of money has become the second-biggest worry, after the state of the economy -- which is expected to be voters' No. 1 concern.

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